In recent years, a telescope and binoculars are required to be compact and lightweight. On the other hand, since a bright optical system is also required, the objective aperture of an optical system tends to be larger. Further, to correct paraxial chromatic aberrations, an objective lens is, for example, made of an anomalous dispersion glass material having large specific gravity, which prevents a compact and lightweight apparatus from being achieved. To address the problem, a proposal has been made to use an erecting optical system in which a glass prism, which is heavy, is replaced with mirrors for reflection (see Patent Literature 1, for example).